The problem with latex products is that rests could tend to clog/harden or partly harden in the room between ball and valve body, giving excess operating torque.

Normal steel or stainless steel would probably be OK (Solvent present ?) for your product.

You could try a Globe - Y-pattern valve, preferably with sharp-edged seat, and check if you get a proper flow and avoid clogging. (Actually I doubdt this, but depending on product consistence)

Alternatively you could try a stainless steel ballvalve with three parts, making it possible to losen the four connecting bolts, take out three of them and swing out the ball-body part for inspection and cleaning/changing.

The painting industry used years ago a sort of open-ended outlet with circle-segment formed sliding plane attached. Closing and opening by contra-formed attached 'gate', thus only suitable for open-ended flowregulating by filling barrels etc.

Did you ever consider a diaphragm valve? They are not a quarter turn to open and close so although it takes a few more cranks on the wheel to operate it won't be quite as hard to operate. Check out www.engvalves.com . Their Dia-Flo valves will probably do the trick. Good luck!

Yes! I should have thought of that! Several suppliers.